The use of ultrasound in applications such as cutting, drilling, abrading, trimming and cleaning has been known for a long time. Its advantages are also well known, mainly the capacity of machining materials in regions of difficult access, where the use of rotary machining processes or those processes requiring high amplitude of displacement is not possible.
By using mechanical vibrations of low amplitude and relatively high frequency, an important characteristic of the ultrasonic processes of cutting, drilling, abrading, trimming and cleaning is the processing of only the material under the direct action of the tool, with minimum influence on the nearby regions, resulting in high precision. Since ultrasound propagates in metallic materials, it is possible to make tools with various shapes and access angles, which permits not only the processing in the form given by the tool, but to do so in regions of difficult access (SU1456098; U.S. Pat. Nos. 4,330,278; 4,505,676).
Ultrasonic tools have a special design that takes into account the ultrasound propagation in the tool material and the determination of a stationary wave pattern of the mechanical vibrations. Generally, a tool is designed to have maximum vibration in its active region and minimum vibration on the holders (WO200029178). As to the tool material, it is important for said material to be a good ultrasound transmitter and have high ultimate strength to ultrasound. This last characteristic of the tool material is highly important, since the processing speed depends on the ultrasound intensity and the maximum intensity of use may be limited by the ultimate strength of the tool material to ultrasound.
The active region of the ultrasonic tool depends on the material to be processed. However, in a significant number of applications, the use of metallic tips from the own base material of the tool is sufficient. In cleaning processes, one can make tips from materials based on resins or plastics. For the cutting, drilling, abrading and trimming processes, the material of the active tip of the tool is required to be harder or more wear resistant than the material to be processed. Thus, the use of active tips of materials different from that of the tool body, or with a coating of harder material on the material of the tool body is a very important development. Nevertheless, these alternatives are limited to the fact that the interface, which connects the hard material to the tool body, must withstand the ultrasound action without breaking.
Particularly for the processing of very hard materials, or those requiring special care, such as stones, ceramics, glasses, bones, dentine, nitrides, carbides, etc., the ultrasonic processes of cutting, drilling, abrading and trimming are usually indicated, but there is a limitation as to the obtainment of tools with active tips having a hardness and strength suitable for such applications. Alternatively, where possible, abrasive powders under the action of less hard tools and also diamond coated tools are used. However, conventional diamond coating processes are inadequate to use in ultrasonic tools. The agglutination of diamond powder with various grain sizes, by electrochemical deposition of nickel, diamond-metal and diamond-resin composites, which are widely used techniques for producing conventional tools, is inadequate to ultrasonic tools, as the diamond grains are easily released from said tools during operation thereof, rapidly exposing the metal of said tool to the surface of the material being processed. In order to overcome these limitations, special alloys using different metals were developed to allow a better wettability of the diamond grains and consequently provide a diamond powder agglutination that is more resistant to ultrasound (SU563280; SU837610). With such modifications it was possible to extend the lives of these tools for some types of applications, without however reaching a desired adequate level.
While CVD diamond coatings have been employed for manufacturing tools, there are no references as to their application in ultrasonic tools (U.S. Pat. Nos. 5,232,568; 5,142,785; 5,376,444; 5,139,372; 4,707,384; 5,022,801; WO09626303; BR9500117).
In some specific constructions of an ultrasonic cutting tool, it is desirable to have the basic body of said tool in molybdenum, since this is a material in which the ultrasound propagates quite well and has high ultimate strength to ultrasound. Also, it is a material that, under certain conditions, allows diamond growth of good quality and relative adherence.
However, in the diamond growth environment, the molybdenum is extensively carburized and transformed into molybdenum carbide, which is highly susceptible to rupture by ultrasound action. Moreover, the adherence that is normally obtained by conventional methods between the diamond film and molybdenum is insufficient for the interface to withstand the ultrasound action, of medium intensity, without breaking.